The objective of CPSB's involvement in this collaborative study is to establish a biological specimen bank within the ongoing Veterans Administration Cooperative Study #380, "Prospective Evaluation of Risk Factors for Large (greater than 1 cm) Colonic Adenomas." This bank will permit the examination of several nutritional and genetic hypotheses bearing on colorectal neoplasia. The Veterans Administration Cooperative Study #380, "Prospective Evaluation of Risk Factors for Large (greater than 1 cm) Colonic Adenomas," is currently being conducted at twelve V.A. sites in the United States. Phase I of the study examines characteristics of and risk factors for the presence of large and small polyps in 3,000 asymptomatic participants undergoing colonoscopy. Phase II involves an examination of factors associated with adenoma recurrence within a five-year followup period among a subset of the original participants (all those with large and small polyps and a subset of polyp-free participants). Specimens will be obtained from approximately 600 participants (an estimated 150 with large adenomas, 150 with small polyps, and 300 without polyps). White cells will be collected for future DNA analysis, and serum will be obtained for analysis of micronutrients or putative colorectal neoplasia markers. Two biopsies of normal-appearing tissue will be obtained from those participants with polyps.